1. Field of the Invention
This invention relates to photosensitive compositions comprising a high molecular weight butadiene/acrylonitrile copolymer and a low molecular weight butadiene polymer, and the use of such compositions as the photosensitive element in flexographic printing plates.
2. Description of the Prior Art
Butadiene/acrylonitrile copolymer binders have been employed previously in photosensitive compositions. U.S. Pat. No. 3,825,430 to Kurka describes a light-sensitive composition containing a continuous phase of a light-sensitive organic material and a discontinuous phase of a finely divided, elastomeric organic compound uniformly distributed through the continuous phase, e.g., a carboxyl-containing, high molecular weight butadiene/acrylonitrile copolymer. The discontinuous phase generally represents 5-50% by weight of the total composition.
Canadian Pat. No. 614,181 to McGraw describes a photopolymerizable composition at least 40% by weight of a butadiene homopolymer or copolymer binder including butadiene/acrylonitrile and butadiene/methacrylic acid copolymers, at least 10% by weight of an addition-polymerizable ethylenically unsaturated compound and 0.001 to 10% by weight of a polymerization initiator.
British Pat. No. 1,358,062 to Uniroyal, Inc. also teaches photosensitive compositions containing at least 40% by weight of a nitrile rubber including butadiene/acrylonitrile copolymers, at least 5% by weight of an addition-polymerizable ethylenically unsaturated compound, and 0.1 to 10% by weight of a polymerization initiator.
British Pat. No. 1,395,822 to Uniroyal, Inc. teaches photopolymerizable compositions comprising at least 40% by weight of an elastomeric monovinylarene/diene block copolymer, at least 5% by weight of a polyethylenically unsaturated ester, and 0.1 to 10% by weight of a polymerization initiator. Optionally, the composition may contain up to 50% by weight of a liquid rubber having a molecular weight of 750 to 3000, for example, butadiene homopolymers or copolymers with acrylonitrile.